Effect of Sintering Condition on the Microstructure and Electrical Properties of Lead-Free (Na_(0.5)K_(0.5))NbO_3 - Bi_(0.5)(Na_(0.95)K_(0.05)_(0.5)TiO_3 Ceramics

摘要

(Na_(0.5)K_(0.5))NbO_3 with 0-5 mole% Bi_(0.5)(Na_(0.95)K_(0.05))_(0.5)TiO_3 has been prepared following the conventional mixed oxide process. It can be concluded that the NKN-BNKT ceramics have orthorhombic structures in the case x< 0.02. With increasing BNKT content (x=0.03 to 0.05), however, the structure changes from orthorhombic to rhombohedral phase. Above results demonstrated that the MPB between orthorhombic and rhombohedral phases exits in the solid solution with the BNKT content of x=0.02. For 0.98(Na_(0.5)K_(0.5))NbO_3-0.02Bi(Na_(0.95)K_(0.05))TiO_3 ceramics, the electromechanical coupling coefficients of the planar mode k_p and the piezoelectric constant d_(33) reach 0.28 and 155 p/CN, respectively, at the sintering of 1100 °C for 3 h. Dielectric and piezoelectric properties have maximum values at the sintering temperature of 1100 °C for 5 h. For 0.98(Na_(0.5)K_(0.5))NbO_3-0.02Bi_(0.5)(Na_(0.95)K_(0.05))_(0.5)TiO_3 ceramics, the electromechanical coupling coefficients of the planar mode kp and the piezoelectric constant d_(33) reach 0.30 and 170, respectively, at the sintering of 1100 °C for 5 h. The effect of prolonging the sintering time to the 0.98(Na_(0.5)K_(0.5))NbO_3-0.02Bi_(0.5)(Na_(0.95)K_(0.05))_(0.5)TiO_3 system is a helpful method on ceramic processing to improve densification and properties..